1. Field of the Invention
The present invention relates to a method of activating a data phase locked loop and an apparatus of operating the same, and more particularly, to a method of activating a data phase locked loop during track-seeking and an apparatus of operating the same.
2. Description of the Prior Art
Small-sized, low-cost and large capacity compact discs capable of storing vast amounts of electronic information, data or video messages have become one of the most important means of storing data in modern society. Common digital optical storage devices include compact discs (CDs), video compact discs (VCDs), or digital versatile discs (DVDs) having various specifications such as DVD-R, DVD-RAM and DVD-RW. An optical device, such as a CD player, uses an optical pick-up to access data stored in a CD. To access the correct data, the optical device is required to seek a corresponding target data track and locate the optical pick-up on the target data track for reading or writing data. Therefore, the ability of performing efficient and accurate track-seeking greatly determines the performance of the optical device and has become a major focus when developing a new optical device.
Optical discs, such as CDs, DVDs and VCDs, include a plurality of continuous tracks for data storage. The continuous tracks, comprising many pits and lands, are formed spirally on the surface of the optical disc. Data is written into the optical disc based on a writing pulse and is embedded on the surface of the optical disc in the form of digital signals. Since a piece of data is usually stored closer to the center of the optical disc, the optical pick-up moves from inner data tracks towards outer data tracks when accessing data stored in the optical disc. However, in applications such as playing songs stored in a CD randomly instead of sequentially, the optical pick-up is often required to move from the current data track to another data track. This action of seeking a target data tack is referred to track-seeking or track-crossing. The optical pick-up does not access data while perform track-seeking. Data is only accessed after the optical pick-up has completed track-seeking and has found the target data track.
Since the inner and outer data tracks of the optical disc have different rotational speeds, the locking time of a data phase locked loop (data PLL) often affects the specification of data access time. The data PLL is an essential part of an optical device and can generate timing pulse signals, based on which the optical device can access data stored in the optical disc. Referring to FIG. 1, a prior art data PLL 10 is described. The data PLL 10 includes a phase detector 13, a frequency detector 14, a charge pump 15, a filter 16, a voltage-controlled oscillator (VCO) 17, and a frequency divider 19. The phase detector 13 and the frequency detector 14 provide the charge pump 15 with an adjusting signal based on phase and frequency differences between an eight-to-fourteen modulation signal EFM measured from the optical disc and a feedback signal EFMCLK. Then, the adjusting signal is processed by the charge pump 15, the filter 16, the VCO 17 and the frequency divider 19 for generating the feedback signal EFMCLK. Finally, the feedback signal EFMCLK is sent to the phase detector 13 and the frequency detector 14 and thereby forms a loop until the frequency and the phase of the feedback signal EFMCLK completely match those of the eight-to-fourteen modulation signal EFM.
Since the pick-up of the optical device is not required to access data during track-seeking, the data PLL 10 remains in a “hold” state, which will be explained later. After the optical device has completed performing track-seeking, the data PLL 10 begins frequency or phase adjustments so that the optical pick-up of the optical device can access data stored in the target data track. Referring to FIG. 2, the operation of the prior art data PLL 10 is described. In FIG. 2, T1-T5 represent data tracks of an optical disc, wherein T1 is a starting data track, T5 is a target data track, T2-T4 are data tracks passed by the optical pick-up when the optical device is performing track-seeking (moving from the data track T1 to the data track T5), RF represents a radio frequency signal of the optical device, TRON represents a track-seeking signal measured from the optical disc, and an arrow indicates the track-seeking direction of the optical device. The track-seeking signal TRON having a low potential indicates that the optical device is performing track-seeking and is not required to access data, while the track-seeking signal TRON having a high potential indicates that the optical device has finished performing track-seeking and is ready for data access. The prior art data PLL 10 determines whether it should perform frequency and phase adjustments based on the potentials of the track-seeking signal TRON: if the track-seeking signal TRON has a low potential, the data PLL 10 remains in the “hold” state in which the frequency and the phase of the signal remains the same as when it is used to access the data track T1 and no adjustment is performed; if the track-seeking signal TRON has a high potential, the data PLL 10 adjusts the frequency and the phase of the signal used to access the target data track T5.
The prior art data PLL 10 performs frequency and phase adjustments after the optical pick-up of the optical device has finished track-seeking and found the target track. The adjustments continue until the phase and the frequency of the feedback signal EFMCLK match those of the eight-to-fourteen modulation signal EFM of the optical disc, and data can then be accessed. Since the data tracks T1 and T5 have different rotational speed, the frequency ranges of signals measured from the data tracks T1 and T5 by the optical pick-up also vary. Therefore, in the prior art optical device, longer time is required for phase and frequency adjustments, resulting in longer data access time and influencing the performance of the optical device.